ABSTRACT Cancer is a leading cause of morbidity and mortality in the United States. tRNA fragments (tRFs) have been found to play a role in cancer pathogenesis. Our lab was one of the first to discover and characterize tRNA fragments, a novel class of small non-coding RNAs, by systematically analyzing publicly available data. Mechanistic insight into the function and regulation of tRFs is essential to understand their role in cancer, and potentially identify pathways for novel therapeutics or patient stratification. We and others have shown that tRFs can regulate gene expression at the post-transcriptional level. Despite some functional characterization of tRFs, there is still a paucity of knowledge regarding tRF regulation. One way to gain insight into the regulation of RNA is to measure RNA decay kinetics. Here, I propose to measure the decay rates of tRFs across species. Elucidation of these parameters will give a better understanding of tRF stability, and will give insight into regulation of tRF levels, a major question in the field. I will determine the regulation of tRF stability at a mechanistic level. I will test whether tRF stability is regulated by various cis features, such as non-template nucleotide additions and secondary structure, and trans features, mainly RNases. Preliminary data suggests that DIS3, the RNase component of the nuclear RNA exosome, is important for regulating tRF levels. Interestingly, DIS3 perturbations are thought to drive many cancers. Taken together, I hypothesize that tRF stability is regulated by cis- and trans-factors, and that DIS3 is a key trans-factor that regulates tRF stability. Finally, I hypothesize that DIS3 dysregulation in cancer promotes aberrant tRF expression, ultimately leading to aberrant tRF-regulated target gene expression and changes in the oncogenic phenotypes of cancer cells. I will pursue several opportunities, described in the proposal, to enhance my preclinical and clinical knowledge, so that I can better integrate my research knowledge with my clinical interests. I will also pursue opportunities to enhance my writing, networking and mentoring skills, so that I can eventually become a successful independent PI as a physician-scientist.